Cardiac resynchronization therapy (CRT) modifies the electrical activation and contractions of the heart's chambers to enhance pumping efficiency. Benefits may include increased exercise capacity and reduced hospitalization and mortality. More particularly, CRT devices operate by affecting the timing of contraction of one or more cardiac chambers relative to one or more other cardiac chambers. For example, contractions of one or more of the ventricle(s) may be timed relative to contraction of the atria, or contractions of the left and right ventricles may be timed relative to one another.
A “fusion” beat occurs when multiple activation signals affect the same cardiac tissue at the same time. For example, electrical fusion between pacing of one ventricle with spontaneous activation of another ventricle (for example, paced left ventricular (LV) activation and intrinsic right ventricular (RV) activation) produces a fusion beat. The generation of fusion beats is a goal of CRT in many circumstances.
Prior systems generally include intracardiac electrodes coupled via transvenous leads to an implanted pulse generator. The leads of such systems are widely known as introducing various morbidities and are prone to eventual conductor and/or insulator failure. Such issues likely reduce usage of CRT within the indicated population of heart failure patients.
Such prior lead systems typically include ventricular and atrial components to facilitate sensing of atrial and ventricular events to enhance CRT timing. For example, in some patients, CRT may be achieved by pacing the left ventricle at a specific time relative to detection of an atrial event. The atrial signal may conduct to the right ventricle (RV) via natural conduction to generate an RV contraction, with paced LV contraction occurring at a desirable time relative to the RV contraction to yield a fusion beat. The interval from the atrial sensed event to the LV pace may be adjusted to enhance cardiac response in prior systems.
Newer generation pacemakers include the leadless cardiac pacemaker (LCP), which can be implanted entirely within the heart and does not require a transvenous (or any) lead. Such devices are commercially available on a limited basis, but are currently indicated for and capable of use in only bradycardia pacing. With further enhancements, the LCP also presents an opportunity to provide an alternative to traditional CRT using transvenous leads. New and alternative systems, devices and methods directed at providing CRT using the LCP are desired.